Re: [PATCH 2/3] dmaengine: rcar-dmac: Add missing dma_descriptor_unmap()

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Thu, Sep 17, 2026 at 09:12:07AM +0200, Wolfram Sang wrote:
> From: Koichiro Den <den@valinux.co.jp>
> 
> Call dma_descriptor_unmap() right after dma_cookie_complete() in the
> threaded IRQ completion path. Without this, streaming DMA mappings
> attached to the descriptor are never released and may eventually exhaust
> DMA mapping resources (e.g. IOVA with an IOMMU or bounce-buffer slots
> with SWIOTLB), leading to dma_map_* failures.

That looks like a horrible API. It pushes a requirement onto drivers to
clean up something done by clients, and is completely undocumented.
Can't those calls be moved somewhere in the DMA engine core ?

> Also ensure dma_descriptor_unmap() is called in rcar_dmac_chan_reinit()
> (error/terminate path) to avoid the same type of leaks.
> 
> Fixes: 87244fe5abdf ("dmaengine: rcar-dmac: Add Renesas R-Car Gen2 DMA Controller (DMAC) driver")
> Signed-off-by: Koichiro Den <den@valinux.co.jp>
> [wsa: added Fixes tag]
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> ---
>  drivers/dma/sh/rcar-dmac.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
> index 5b54f1c4ce15..9155bceb723b 100644
> --- a/drivers/dma/sh/rcar-dmac.c
> +++ b/drivers/dma/sh/rcar-dmac.c
> @@ -844,6 +844,7 @@ static void rcar_dmac_chan_reinit(struct rcar_dmac_chan *chan)
>  
>  	list_for_each_entry_safe(desc, _desc, &descs, node) {
>  		list_del(&desc->node);
> +		dma_descriptor_unmap(&desc->async_tx);
>  		rcar_dmac_desc_put(chan, desc);
>  	}
>  }
> @@ -1654,6 +1655,7 @@ static irqreturn_t rcar_dmac_isr_channel_thread(int irq, void *dev)
>  		desc = list_first_entry(&chan->desc.done, struct rcar_dmac_desc,
>  					node);
>  		dma_cookie_complete(&desc->async_tx);
> +		dma_descriptor_unmap(&desc->async_tx);
>  		list_del(&desc->node);
>  
>  		dmaengine_desc_get_callback(&desc->async_tx, &cb);

-- 
Regards,

Laurent Pinchart